1. Field of the Invention
The present invention relates in general to a fast running mode conversion device for magnetic recording and reproducing apparatus and, more particularly, to a structural improvement in such a mode conversion device for simplifying the construction of the device and lengthening the expected life span of the device.
2. Description of the Prior Art
With reference to FIG. 1, there is shown a typical reel drive mechanism for a magnetic recording and reproducing apparatus having a fast running mode conversion device. As shown in this drawing, the reel drive mechanism includes a clutch unit 40 which in turn comprises a reel drive gear 54 rotatably fitted over a shaft 42, which shaft 42 is fixedly fitted to and extends downwardly from a base plate 1. The reel drive gear 54 gears into a tape supply reel gear (not shown) of a tape supply reel assembly (not shown). Fitted over the shaft 42 under the reel drive gear 54 is a clutch gear 52. A pair of friction members 55 of the hollow disc type are disposed on and under the clutch gear 52 respectively. Fitted over the shaft 42 under the lower friction member 55 is a hollow disc 56. In order to bias the hollow disc 56 toward the reel drive gear 54 and to generate desired frictional force in the two friction members 55, a coil spring 57 is disposed about the shaft 42 under the disc 56. The lower end of the coil spring 57 is stopped by a fast running mode gear 53 which will be rotated at the same time of rotation of the reel drive gear 54. The position of the fast running mode gear 53 on the shaft 42 is retained by a spring washer 53a fitted over the shaft 42.
An idler unit 60 is placed by the right side of the clutch unit 40 as shown in FIG. 1. The idler unit 60 includes an idler arm 61 whose one end is rotatably fitted over a gear pulley shaft 60a, which shaft 60a is fixedly fitted to and extends downwardly from the base plate 1. The other end of the idler arm 61 is rotatably fitted over an idler shaft 61a by the side of the clutch unit 40, so that the idler arm 61 rotatably support an idler 62 which is fitted over the idler shaft 61a under the idler arm 61. Here, fitted over the lower end of the gear pulley shaft 60a is a gear pulley 68. The idler arm 61 and the idler 62 are coupled to each other by a piece of felt 65, a coil spring 64 and a washer 66, so that desired frictional torque is generated by all of the felt 65, the coil spring 64 and the washer 66 in response to motion of the idler arm 61.
The reel drive mechanism also includes a tape fast running mode conversion device 70 (hereinbelow, referred to simply as "the mode conversion device") placed on the top surface of the base plate 1. As best seen in FIG. 2, the mode conversion device 70 comprises a lifting lever 71. The lifting lever 71 is pivotally mounted on a bracket 41 so that the lever 71 selectively partially comes into contact with the top surface of the base plate 1. The mode conversion device 70 also comprises a turning lever 72 which is rotatably mounted on a shaft 72f fixed to the top surface of the base plate 1. The turning lever 72 is driven by a drive cam 76. The mode conversion device 70 further comprises a biasing member 73 placed on the turning lever 72. The biasing member 73 drives the lifting lever 71 in accordance with turning motion of the turning lever 72. The biasing member 73 is a nonlinear slender member whose center bent portion is rested against a pin 72b provided on the center portion of the turning lever 72. One end portion of the biasing member 73 is caught by a first stopper 72c provided on the from portion of the turning lever 72 while the other end portion of the biasing member 73 is caught by a second stopper 72d provided on the rear portion of the turning lever 72. The biasing member 73 thus elastically lies across the turning lever 72 with the one end of the member 73 projecting out of the front end of the lever 72 to a length L.
The drive cam 76 is provided with an annular cam slot 77 of a predetermined depth. This cam slot 77 extends beside the outer edge of the cam 76. A cam pin 75 which is provided on the end of the turning lever 72 is movably received in the cam slot 77 of the drive cam 76. As shown in FIG. 2, the turning lever 72 is biased by a tension coil spring 74 so that the lever 72 is biased so as to be turned clockwise about its rotating shaft 72f (FIG. 1). The one end of the spring 74 is connected a spring hook 72a provided on the rear end of the lever 72 but the other end of the spring 74 is connected to an appropriate portion of the base plate 1.
In operation of the above reel drive mechanism, the turning lever 72 of the mode conversion device 70 is turned in accordance with rotating motion of the drive cam 76. As a result of the turning motion of the turning lever 72, the biasing member 73 pushes the lifting lever 71, thus to make the idler arm 61 of the idler unit 60 be lowered toward the gear pulley 68 (see FIG. 1 ). As the idler arm 61 is lowered as described above, a small idler gear 62a of the idler 62 coupled to the arm 61 is disengaged from the clutch gear 52. At this time, a large idler gear 62b of the idler 62 is engaged with the fast running mode gear 53, thus to start a fast running mode, that is, the FF mode or the REW mode.
That is, when the idler 62 is engaged with the clutch gear 52, the drive force of a motor (not shown) is transmitted, with a torque less than the predetermined level because of slip, to the reel drive gear 54 gearing into an output gear 51. In this case, a reel table (not shown) is rotated at a low speed in the same manner as a reproducing mode, that is, the normal-direction reproducing mode or the reverse-direction reproducing mode. However, when the idler 62 is engaged with the fast running mode gear 53, the drive force of the motor is transmitted to the reel drive gear 54 with no slip. The reel table in this state is thus rotated at a high speed, thus to start a desired fast running mode.
As described above, the typical fast mode conversion device of the reel drive mechanism includes the biasing member 73 for pushing and driving the lifting lever 71. The mode conversion device also includes the tension coil spring 74 for elastically returning both the turning lever 72 and the biasing member 73. The mode conversion device should be thus complicated in its construction. In addition, the nonlinear shape of the biasing member 73 is very complicated. The bending portion of the biasing member 73, which bending portion is applied with bending force when pushing the lifting lever 71, is short so that the biasing member 73 should be overloaded when pushing and driving the lifting lever 71. That is, the length L between the front end of the biasing member 73 and the first stopper 72c provided on the front portion of the turning lever 72 is short so that driving of the lifting lever 71 should be attended with large force. Another problem of the mode conversion device resides in that the biasing member 73 is such a simple cantilever that the member 73 is easily deformed and deteriorates the operational reliability of the magnetic recording and reproducing apparatus.